Thank you, so what is auto used for then?
According to Ecotech Marine:
"Auto mode schedules dosing specific to what additive or solution is being dosed. This mode utilizes standard dosing practices and known water parameter changes in a reef tank based on light cycle and biological activity. The Versa™ does not determine dosing volume, that requires testing and tuning. It will however, schedule dosing based on the salt or additive selected."
Basically, in this mode depending of the additive (Cal, Alk, Mag) the pump take the decision to when during the day is better to dose that solution (morning, midday, night, etc). you just set the quantity X day and the pump will take the decision when.
Manually you have more control, you can program individual schedule (every hr, two hr, etc) or one big schedule telling the pump to dose XX mg in XX time.
Personally I dose one time per hr (24 dose) at the beginning setting up the whole 24 point is a paint, but then you will have more control to when and to make sure your Cal,Alk and Mag dosing dont cross each other. Plus after using the alkatronic to monitor Alk, Im dosing around 70% of my dosing requirements when the lights are on. This keep my Alk +/- .20 during 24 hr.